Life-Span of Classical Solutions to a Semilinear Wave Equation with Time-Dependent Damping

. This paper is concerned with the Cauchy problem for a semilinear wave equation with a time-dependent damping. In case that the space dimension n = 1 and the nonlinear power is bigger than 2, the life-span (cid:101) T ( ε ) and global existence of the classical solution to the problem has been investigated in a unified way. More precisely, with respect to different values of an index K , which depends on the time-dependent damping and the nonlinear term, the life-span (cid:101) T ( ε ) can be estimated below by ε − p 1 − K , e ε − p or + ∞ , where ε is the scale of the compact support of the initial data.